Aztreonam is a monobactam antibiotic disclosed in U.S. Pat. No. 4,775,670, which is incorporated by reference herein in its entirety. Aztreonam has the chemical name (Z)-2-[[[(2-amino-4-thiazolyl)[[(2S,-3S)-2-methyl-4-oxo-1-sulfo-3-azetidinyl]carbamoyl]methylene]amino]oxy]-2-methylpropionic acid. Aztreonam is also known as [3S-[3α(Z),4β]]-3-[[(2-amino-4-thiazolyl)[(1-carboxy-1-methylethoxy)imino]acetyl]amino]-4-methyl-2-oxo-1-azetidinesulfonic acid and (2S, 3S)-3-[[2-[2-amino-4-thiazolyl]-(Z)-2[(1-carboxy-1-methylethoxy)imino]acetyl]amino]-4-methyl-2-oxo-1-azetidine-1-sulfonic acid.
Aztreonam has the structure:

Aztreonam is known to exist in various polymorphic forms including the α, β, δ, and γ forms.
U.S. Pat. No. 4,775,670 discloses a process for making Aztreonam, a compound of formula I:
The process includes acylating a compound of formula IV:

The acylation entails reacting a compound of formula IV with a carboxylic acid or the corresponding carboxylic acid halide or carboxylic acid anhydride (R1—OH) in the presence of a carbodiimide such as dicyclohexylcarbodiimide and a substance capable of forming an active ester in situ such as N-hydroxybenzotriazole. U.S. Pat. No. 4,775,670 discloses that when the acyl group (R1) contains reactive functional groups, such as amino or carboxyl groups, it may be necessary to first protect those functional groups, then carry out the acylation reaction, and finally deprotect the resulting product. The deprotection is carried out by reaction of the acylation product with trifluoroacetic acid in the presence of anisole under anhydrous conditions.
Similarly, U.S. Pat. No. 4,946,838 discloses a process for making crystalline anhydrous Aztreonam comprising reacting the diphenylmethyl ester of Aztreonam ([3S-[3β(Z),4α]]-3-[[(2-amino-4-thiazolyl)[(1-diphenylmethoxycarbonyl-1-methylethoxy)imino]acetyl]amino]-4-methyl-2-oxo-1-azetidinesulfonic acid) with trifluoroacetic acid in the presence of anisole under anhydrous conditions to produce the α-form of Aztreonam. The α-form is recrystallized from an anhydrous organic solvent to produce the β-form of Aztreonam. The β-form is anhydrous, substantially non-hygroscopic and more stable than the α-form.
U.S. Pat. No. 5,254,681 discloses a process for preparing monobactams of formula (I):
wherein R is acyl. The process comprises acylating azetidin with 2-(2-amino-4-thiazolyl)-2-(Z)-(alkoxyimino) acetic acid in the presence of 1-hydroxy-benzotriazole and dicyclohexylcarbodiimide.
U.S. Pat. No. 5,194,604 discloses a process and intermediates for making beta-lactams having aminothiazole(iminooxyacetic acid)acetic acid sidechains of formula (I), such as Aztreonam. The process comprises acylating a compound of formula III:
with a compound of formula (II):
in which R7 is
wherein
is a 4, 5, 6 or 7 membered heterocyclic ring having at least one nitrogen atom in the ring or such a group fused to a phenyl or substituted phenyl ring, to form a compound of formula (I):
wherein R1–R6 are as defined in U.S. Pat. No. 5,194,604.
U.S. Pat. No. 4,652,651, which is incorporated by reference herein in its entirety, discloses a process for making 1-sulpho-2-oxoazetidine derivatives of the formula (I):
in which Het is an optionally amino-substituted, 5- or 6-membered, aromatic heterocycle containing 1 or 2 nitrogen atoms and optionally also an oxygen or sulphur atom, R1 may be lower alkoxycarbonyl-lower alkyl and R2 may be lower alkyl. The process entails acylating a compound of formula (II):
in which R20 equals R2 and R3 is hydrogen or sulpho, with a thioester of the formula (III):
in which Het is as above and R10 has any of the values of R1. U.S. Pat. No. 4,652,651 discloses that where R10 is a lower alkoxycarbonyl-lower alkyl group, for example the t-butoxycarbonylmethyl group, this can be converted, if desired, into the corresponding carboxylower alkyl group by treatment with a strong acid such as trifluoroacetic acid (optionally in the presence of anisole), hydrochloric acid or p-toluenesulphonic acid at a low temperature such as −10° C. to room temperature.
There remains a need in the art for a process of making Aztreonam which does not require anhydrous reaction conditions and which also enables high yield and high purity. The present invention answers this need.